Effects of Future Climate Projections on Stream Temperatures and Fish Thermal Habitat for Upper Midwest and Great Lakes Streams

Climate change projections in the Upper Midwest indicate warmer and wetter trends, with a potential for altered hydrologic functions of surface and ground water resources including elevated stream temperature, decreased minimum flows, and increased peak flows. These changes can have profound effects on aquatic ecosystems by altering instream habitat, resulting in changes in fish distributions and community composition.  We integrated regional downscaled climate projections with an artificial neural network (ANN) stream temperature model to estimate the effect of climatic change on stream temperature. The ANN model predicts daily mean summertime stream temperature for 38,421 stream segments of the 1:100,000 scale National Hydrography Data in Wisconsin. Simulated air temperature and precipitation from 10 climate models were integrated with the ANN model and a related Soil Water Balance model to estimate future stream temperatures under one emission scenario (A1B1) for two time periods (2046 - 2065 and 2081 - 2100). For the first time period (2046 – 2065), the maxium change in July mean stream temperature ranged from 0.87 C to 2.95 C (median = 1.45 C) across all ten climate models for individual stream segments when compared to predictions under the current time period (1990 – 2008). The minimum change in July mean stream temperature ranged from 0.07 C to 0.41 C (median = 0.12 C) and the average change ranged from 0.63 C to 2.25 C (median = 1.03 C). For the second time period (2081 – 2100), the maxium change in July mean stream temperature ranged from 0.77 C to 4.28 C (median = 2.58 C) across all ten climate models for individual stream segments when compared to predictions under the current time period. The minimum change in July mean stream temperature ranged from 0.09 C to 0.41 C (median = 0.18 C) and the average change ranged from 0.53 C to 2.77 C (median = 1.71 C). We recognize the predicted stream temperatures may vary greatly depending on the emission scenario and models used; the results presented here represent one possibility.  However, the relative change in stream temperatures can be used by managers to help prioritize stream segments or habitats in which to apply adaptation strategies to address potential climate change impacts on aquatic ecosystems.